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Why Do Some Volcanoes Erupt Gently? — Volcano erupting with glowing lava and smoke at night.

Why Do Some Volcanoes Erupt Gently?CEFR B1

24 Nov 2025

Adapted from ETH Zurich, Futurity CC BY 4.0

Photo by Wolfgang Hasselmann, Unsplash

AI-assisted adaptation of the original article, simplified for language learners.

The explosiveness of a volcano is influenced by gas bubbles in the magma. Traditionally, scientists believed bubbles formed only when pressure dropped. However, new research shows that shear forces—movements in the magma—also play a crucial role in bubble formation.

In volcanic conduits, the magma moves at different speeds due to friction. This creates shear forces that can help form gas bubbles, allowing for a calmer flow of magma. A prime example is Mount St. Helens, where despite gas-rich magma, the initial eruption featured slow lava flow due to these forces.

Observations from experiments and computer simulations suggest that understanding these shear forces is vital for improving models that predict volcanic eruptions. This research helps explain why some viscous magmas flow out gently, highlighting the complex behaviors of gases within magma.

Difficult words

  • explosivenessThe ability to explode with force.
  • influenceTo have an effect on something.
    influenced
  • shearA type of force that causes layers to slide.
  • viscousThick and sticky, not easily flowing.
  • eruptionAn explosion of a volcano.

Tip: hover, focus or tap highlighted words in the article to see quick definitions while you read or listen.

Discussion questions

  • How might this research change how we monitor volcanoes?
  • What are other factors that might affect volcanic eruptions?
  • Can you think of other natural phenomena influenced by similar forces?

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